Process for preparing C3-6(hydro)fluoroalkenes by dehydrohalogenating C3-6 halo(hydro) fluoroalkanes in the presence of a zinc chromia catalyst

ABSTRACT

A process for preparing 2,3,3,3-tetrafluoropropene (CF 3 CF═CH 2 ). 3,3,3-trifluoro-2-chloropropene (CF 3 CCl═CH 2 ) is fluorinated with HF in the vapour phase in the presence of a chromia-containing catalyst to produce an intermediate composition 1,1,1,2,2-pentafluoropropane (CF 3 CF 2 CH 3 ), which is dehydrofluorinated to produce CF 3 CF═CH 2 .

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/876,384 filed 6 Oct. 2015, which is a continuation of U.S. patentapplication Ser. No. 14/043,191 filed 1 Oct. 2013, which is acontinuation of U.S. patent application Ser. No. 12/311,540 filed 16Oct. 2009, now U.S. Pat. No. 8,546,623, issued 1 Oct. 2013, which wasthe US National Phase of PCT Application No. PCT/GB2007/003749 filed 3Oct. 2007, which claimed priority to Great Britain Application No.0619505.1 filed 3 Oct. 2006 and Great Britain Application No. 0706980.0filed 11 Apr. 2007.

BACKGROUND OF THE INVENTION

The present invention relates to a process for preparing(hydro)fluoroalkenes and particularly to a process for preparing C₃₋₆(hydro)fluoroalkenes by the dehydrohalogenation of ahydro(halo)fluoroalkane.

The known processes for preparing (hydro)fluoroalkenes typically sufferfrom disadvantages such as low yields, and/or the handling of toxicand/or expensive reagents, and/or the use of extreme conditions, and/orthe production of toxic by-products. This is exemplified by consideringthe known methods for producing C₃₋₆ (hydro)fluoroalkenes such as2,3,3,3-tetrafluoropropene. Methods for the preparation of2,3,3,3-tetrafluoropropene have been described in, for example, JournalFluorine Chemistry (82), 1997, 171-174. In this paper,2,3,3,3-tetrafluoropropene is prepared by the reaction of sulphurtetrafluoride with trifluoroacetylacetone. However, this method is onlyof academic interest because of the hazards involved in handling thereagents and their expense. Another method for the preparation of2,3,3,3-tetrafluoropropene is described in U.S. Pat. No. 2,931,840. Inthis case, pyrolysis of Cl chlorofluorocarbons with or withouttetrafluoroethylene was purported to yield 2,3,3,3-tetrafluoropropene.However, the yields described were very low and again it was necessaryto handle hazardous chemicals under extreme conditions. It would also beexpected that such a process would produce a variety of very toxicby-products. In addition to addressing the disadvantages of the knownmethods, it would be desirable to provide new methods for thepreparation of (hydro)fluoroalkenes that use only readily availablefeedstocks.

It is also known from U.S. Pat. No. 5,679,875 (Daikin) that1,1,1,2,3-pentafluoropropene can be prepared by contacting anddehydrofluorinating 1,1,1,2,3,3-hexafluoropropane in the gaseous statewith trivalent chromium oxide or partially fluorinated trivalentchromium oxide, optionally in the presence of oxygen.

The listing or discussion of a prior-published document in thisspecification should not necessarily be taken as an acknowledgement thatthe document is part of the state of the art or is common generalknowledge.

SUMMARY OF THE INVENTION

The present invention addresses the foregoing deficiencies of the knownroutes for preparing (hydro)fluoroalkenes by providing a process forpreparing a C₃₋₆ (hydro)fluoroalkene comprising dehydrohalogenating aC₃₋₆ hydro(halo)fluoroalkane in the presence of a zinc/chromia catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of the dehydrofluorination ofCF3CFClCH2Cl at a 15:1 HF to Organics ratio at various reactortemperatures.

FIG. 2 is a graphical representation of the dehydrofluorination ofCF3CClCH2Cl at a 5:1 HF to Organics ratio at various reactortemperatures.

FIG. 3 is a graphical representation of the dehydrofluorination ofCF3CF2CH3 Cl at a 5:1 HF to Organics ratio at various reactortemperatures.

FIG. 4 is a graphical representation of the dehydrofluorination of 236eaat various temperatures and various feeds of HF.

FIG. 5 is a graphical representation of the dehydrofluorination of 236cbat various temperatures and various feeds of HF.

FIG. 6 is a graphical representation of the yield of Z-1225ye at a feedrate of 6HF:1 236ea over various run times.

FIG. 7 is a graphical representation of the yield of Z-1225ye at avarious feed rates of 6HF:1 236ea, depicting the fouling rate of thesefeed rates over various run times.

FIG. 8 is a graphical representation of the impact of various catalystformulations on the yield of Z-1225ye and fouling rates using theseformulations over various run times.

FIG. 9 depicts an analysis of a chromia catalyst containing no zincusing differential scanning calorimetry.

FIG. 10 provides a graphical representation of

the conversion of R-236ea-R-1225ye over time, with coking as a functionof pressure.

FIG. 11 provides a graphical representation of the conversion ofR-236ea-R-1225ye over time, with selectivity over cycle as a function ofpressure.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Typically, the process comprises contacting the hydro (halo)fluoroalkanewith or without hydrogen fluoride (HF) in the vapour or liquid phase andmay be carried out at a temperature of from −70 to 400° C. In certainpreferred embodiments, the process may be carried out with no co-feed ofHF. The process may be carried out at atmospheric sub- or superatmospheric pressure, preferably from about 0 to about 30 bara.

Preferably, the hydro(halo)fluoroalkane is contacted with or without HFin the vapour phase at a temperature of from 200 to 360° C., morepreferably from 240 to 320° C. Preferably, the process is conducted at apressure of from 5 to 20 bar. Of course, the skilled person willappreciate that the preferred conditions (e.g. temperature, pressure andcatalyst) for conducting the process of the invention may vary dependingon the nature of the hydro(halo)fluoroalkane being converted to(hydro)fluoroalkene. In certain preferred embodiments, for example wherethe catalyst contains 1% to 10% by weight of the catalyst of zinc, theprocess may be beneficially carried out at a pressure of 0 to 5 bara,conveniently 1 to 5 bara.

The process of the invention can be carried out in any suitableapparatus, such as a static mixer, a stirred tank reactor or a stirredvapour-liquid disengagement vessel. The process may be carried outbatch-wise or continuously. Either the batch-wise process or thecontinuous process may be carried out in a “one-pot” fashion, or usingtwo or more than discrete reaction zones and/or reaction vessels.

The dehydrofluorination can be carried out in the absence of HF but itmay be desirable in certain embodiments to use some HF in order toprevent and/or retard excessive decomposition of the organic feed and/orcoking of the catalyst. Typically, the HF:organics ratio in the processof the invention if HF is utilised will range from about 0.01:1 to about50:1, preferably from about 0.1:1 to about 40:1, more preferably fromabout 0.5:1 to about 30:1, such as from about 1:1 to about 20:1, forexample from about 2:1 to about 15:1 (e.g. from about 5:1 to about10:1). The skilled person will appreciate that in a multi-stage processthe preferred conditions and ratio may vary from step to step and wouldbe able to select a suitable ratio.

The preferred aspects of the invention have been found to vary at leastaccording to the nature of the catalyst, and the pressure at which theprocess is carried out.

By the term “zinc/chromia catalyst” we mean any catalyst comprisingchromium or a compound of chromium and zinc or a compound of zinc. Such,catalysts are known in the art, see for example EP-A-05 02 605,EP-A-0773061, EP-A-0957 07 4 and WO 98/10862. However, the presentinventors have surprisingly found that zinc/chromia catalysts may beused promote the dehydrohalogenation of C₃₋₆ hydro(halo)fluoroalkanes toproduce C₃₋₆ (hydro)fluoroalkenes.

Typically, the chromium or compound of chromium present in the catalystsof the invention is an oxide, oxyfluoride or fluoride of chromium such,as chromium oxide.

The total amount of the zinc or a compound of zinc present in thecatalysts of the invention is typically from about 0.01% to about 25%,preferably 0.1% to about 25%, conveniently 0.01% to 6% zinc, and in someembodiments preferably 0.5% by weight to about 25% by weight of thecatalyst, preferably from about 1 to 10% by weight of the catalyst, morepreferably from about 2 to 8% by weight of the catalyst, for exampleabout 4 to 6% by weight of the catalyst.

In other embodiments, the catalyst conveniently comprises 0.01% to 1%,more preferably 0.05% to 0.5% zinc.

The preferred amount depends upon a number of factors such as the natureof the chromium or a compound of chromium and/or zinc or a compound ofzinc and/or the way in which the catalyst is made. These factors aredescribed in more detail hereinafter.

It is to be understood, that the amount of zinc or a compound of zincquoted herein refers to the amount of elemental zinc, whether present aselemental zinc or as a compound of zinc.

The catalysts used in the invention may include an additional metal orcompound thereof. Typically, the additional metal is a divalent ortrivalent metal, preferably selected from nickel, magnesium, aluminiumand mixtures thereof. Typically, the additional metal is present in anamount of from 0.01% by weight to about 25% by weight of the catalyst,preferably from about 0.01 to 10% by weight of the catalyst. Otherembodiments may comprise at least about 0.5% by weight or at least about1% weight of additional metal.

The zinc/chromia catalysts used in the present invention may beamorphous. By this we mean that the catalyst does not demonstratesubstantial crystalline characteristics when analysed by, for example,X-ray diffraction.

Alternatively, the catalysts may be partially crystalline. By this wemean that from 0.1 to 50% by weight of the catalyst is in the form ofone or more crystalline compounds of chromium and/or one or morecrystalline compounds of zinc. If a partially crystalline catalyst isused, it preferably contains from 0.2 to 25% by weight, more preferablyfrom 0.3 to 10% by weight, still more preferably from 0.4 to 5% byweight of the catalyst in the form of one or more crystalline compoundsof chromium and/or one or more crystalline compounds of zinc.

During use in a dehydrohalogenation reaction the degree of crystallinitymay change. Thus it is possible that a catalyst of the invention thathas a degree of crystallinity as defined above before use in adehydrohalogenation reaction and will have a degree of crystallinityoutside these ranges during or after use in a dehydrohalogenationreaction.

The percentage of crystalline material in the catalysts of the inventioncan be determined by any suitable method known in the art. Suitablemethods include X-ray diffraction (XRD) techniques. When x-raydiffraction is used the amount of crystalline material such as theamount of crystalline chromium oxide can be determined with reference toa known amount of graphite present in the catalyst (eg the graphite usedin producing catalyst pellets) or more preferably by comparison of theintensity of the XRD patterns of the sample materials with referencematerials prepared from suitable internationally recognised standards,for example NIST (National institute of Standards and Technology)reference materials.

The catalysts of the invention typically have a surface area of at least50 m²/g and preferably from 70 to 250 m²/g and most preferably from 100to 200 m²/g before it is subjected to pre-treatment with a fluoridecontaining species such as hydrogen fluoride or a fluorinatedhydrocarbon. During this pre-treatment, which is described, in moredetail hereinafter, at least some of the oxygen atoms in the catalystare replaced by fluorine atoms.

The catalysts of the invention typically have an advantageous balance oflevels of activity and selectivity. Preferably, they also have a degreeof chemical robustness that means that they have a relatively longworking lifetime. The catalysts of the invention preferably also have amechanical strength that enables relatively easy handling, for examplethey may be charged to reactors or discharged from reactors using knowntechniques.

The catalysts of the invention may be provided in any suitable formknown in the art. For example, they may be provided in the form ofpellets or granules of appropriate size for use in a fixed bed or afluidised bed. The catalysts may be supported or unsupported. If thecatalyst is supported, suitable supports include AlF3, fluorinatedalumina or activated carbon.

The catalysts of the invention include promoted forms of such catalysts,including those containing enhanced Lewis and/or Brönsted acidity and/orbasicity.

The amorphous catalysts which may be used in the present invention canbe obtained by any method known in the art for producing amorphouschromia-based catalysts. Suitable methods include co-precipitation fromsolutions of zinc and chromium nitrates on the addition of ammoniumhydroxide. Alternatively, surface impregnation of the zinc or a compoundthereof onto an amorphous chromia catalyst can be used.

Further methods for preparing the amorphous zinc/chromia catalystsinclude, for example, reduction of a chromium (VI) compound, for examplea chromate, dichromate, in particular ammonium dichromate, to chromium(III), by zinc metal, followed by co-precipitation and washing; ormixing as solids, a chromium (VI) compound and a compound of zinc, forexample zinc acetate or zinc oxalate, and heating the mixture to hightemperature in order to effect reduction of the chromium (VI) compoundto chromium (III) oxide and oxidise the compound of zinc to zinc oxide.

The zinc may be introduced into and/or onto the amorphous chromiacatalyst in the form of a compound, for example a halide, oxyhalide,oxide or hydroxide depending at least to some extent upon the catalystpreparation, technique employed. In the case where amorphous catalystpreparation is toy impregnation of a chromia, halogenated chromia orchromium oxyhalide, the compound is preferably a water-soluble salt, forexample a halide, nitrate or carbonate, and is employed as an aqueoussolution or slurry. Alternatively, the hydroxides of zinc and chromiummay be co-precipitated (for example by the use of a base such as sodiumhydroxide or ammonium hydroxide) and then converted to the oxides toprepare the amorphous catalyst. Mixing and milling of an insoluble zinccompound with the basic chromia catalyst provides a further method ofpreparing the amorphous catalyst precursor. A method for makingamorphous catalyst based on chromium oxyhalide comprises adding acompound of zinc to hydrated chromium halide.

The amount of zinc or a compound of zinc introduced to the amorphouscatalyst precursor depends upon the preparation method employed. It isbelieved that the working catalyst has a surface containing cations ofzinc located in a chromium-containing lattice, for example chromiumoxide, oxyhalide, or halide lattice. Thus the amount of zinc or acompound of zinc required is generally lower for catalysts made byimpregnation than for catalysts made by other methods such asco-precipitation, which also contain the zinc or a compound of zinc innon-surface locations.

Any of the aforementioned methods, or other methods, may be employed forthe preparation of the amorphous catalysts which may be used in theprocess of the present invention.

The catalysts described herein are typically stabilised by heattreatment before use such that they are stable under the environmentalconditions that they are exposed to in use. This stabilisation is oftena two-stage process. In the first stage, the catalyst is stabilised byheat treatment in nitrogen or a nitrogen/air environment. In the art,this stage is often called “calcination”. Fluorination catalysts arethen typically stabilised to hydrogen fluoride by heat treatment inhydrogen fluoride. This stage is often termed “pre-fluorination”.

The present inventors have found that by careful control of theconditions under which these two heat treatment stages are conducted,crystallinity can be induced into the catalyst to a controlled degree.

For example, an amorphous catalyst may be heat treated at a temperatureof from about 300 to about 600° C., preferably from about 400 to 600°C., more preferably from 500 to 590° C., for example 520, 540, 560 or580° C. for a period of from about 1 to about 12 hours, preferably forfrom about 2 to about 8 hours, for example about 4 hours in a suitableatmosphere. Suitable atmospheres under which this heat treatment can beconducted include an atmosphere of nitrogen or an atmosphere having anoxygen level of from about 0.1 to about 10% v/v in nitrogen. Otheroxidizing environments could alternatively be used. For example,environments containing suitable oxidizing agents include, but are notlimited to, those containing a source of nitrate, CrO₃ or O₂ (forexample air). This heat treatment stage can be conducted in addition toor instead of the calcining stage that is typically used in the priorart to produce amorphous catalysts.

Conditions for the pre-fluorination stage can be selected so that theydo not substantially introduce crystallinity into the catalyst. This maybe achieved by heat treatment of the catalyst precursor at a temperatureof from about 200 to about 500° C., preferably from about 250 to about400° C. at atmospheric or super atmospheric pressure for a period offrom about 1 to about 16 hours in the presence of hydrogen fluoride,optionally in the presence of another gas such as nitrogen.

Conditions for the pre-fluorination stage can be selected so that theyinduce a change in the crystallinity of the catalyst or so that they donot induce such a change. The present inventors have found that heattreatment of the catalyst precursor at a temperature of from about 250to about 500° C., preferably from about 300 to about 400° C. atatmospheric or super atmospheric pressure for a period of from about 1to about 16 hours in the presence of hydrogen fluoride, optionally inthe presence of another gas such as air, can produce a catalyst in whichthe crystallinity is as defined above, for example from 0.1 to 8.0% byweight of the catalyst (typically from 0.1 to less than 8.0% by weightof the catalyst) is in the form of one or more crystalline compounds ofchromium and/or one or more crystalline compounds of the at least oneadditional metal.

The skilled person will appreciate that by varying the conditionsdescribed above, such as by varying the temperature and/or time and/oratmosphere under which the heat treatment is conducted, the degree ofcrystallinity of the catalyst may be varied. Typically, for example,catalysts with higher degrees of crystallinity (e.g. from 8 to 50% byweight of the catalyst) may be prepared by increasing the temperatureand/or increasing the calcination time and/or increasing the oxidisingnature of the atmosphere under which the catalyst pre-treatment isconducted.

The variation of catalyst crystallinity as a function of calcinationtemperature, time and atmosphere is illustrated by the following tableshowing a series of experiments in which 8 g samples of a 6% Zn/chromiacatalyst were subjected to calcination across a range of conditions andthe level of crystallinity induced determined by X-Ray diffraction.

Calcination Calcination Atmosphere % Cryst Time (t, Temperaturenitrogen: air Cr₂O₃ hrs) (T, ° C.) (D, v/v) Content 4 400.0 15 1 4 400.015 1 2 450.0 20 9 6 350.0 20 0 2 450.0 10 18 2 350.0 10 0 6 450.0 20 206 350.0 10 0 6 450.0 10 30 4 400.0 15 1 2 350.0 20 0

The pre-fluorination treatment typically has the effect of lowering thesurface area of the catalyst. After the pre-fluorination treatment thecatalysts of the invention typically have a surface area of 20 to 200m²/g, such as 50 to 150 m²/g, for example less than about 100 m² /g.

In use, the catalyst may be regenerated or reactivated periodically byheating in air at a temperature of from about 300° C. to about 500° C.Air may be used as a mixture with an inert gas such as nitrogen or withhydrogen fluoride, which emerges hot from the catalyst treatment processand may be used directly in fluorination processes employing thereactivated catalyst.

Unless otherwise stated, as used herein, a (hydro)fluoroalkene is analkene in which at least one of the hydrogen atoms has been replaced byfluorine.

Unless otherwise stated, as used herein, a hydro(halo)fluoroalkane is analkane in which at least one but not all hydrogen atom has been replacedby a fluorine atom and optionally at least one hydrogen atom has beenreplaced by a halogen selected from chlorine, bromine and iodine. Thus,hydro(halo)fluoroalkanes contain at least one hydrogen, at least onefluorine and optionally at least one halogen selected from chlorine,bromine and iodine. In other words, the definition of ahydro(halo)fluoroalkane includes a hydrofluoroalkane, i.e., an alkane inwhich at least one but not all of the hydrogen atoms have been replacedby fluorine.

Unless otherwise stated, as used herein, any reference to a (C₃₋₆)(hydro)fluoroalkene, hydrofluoroalkane or hydro(halo)fluoroalkane refersto a (hydro)fluoroalkene, hydro fluoroalkane or hydro(halo)fluoroalkanehaving from 3 to 6 carbon atoms, i.e. hydro(halo)fluoro-propane, butane,pentane or hexane or a (hydro)fluoro-propene, butene, pentene or hexene.

The (hydro)fluoroalkenes produced by the process of the inventioncontain a double bond and may thus exist as E (entgegen) and Z(zusammen) geometric isomers about each individual double bond. All suchisomers and mixtures thereof are included within the scope of theinvention.

Unless otherwise stated, as used herein, by the term“dehydrohalogenation” (or dehydrohalogenating), we refer to the removalof hydrogen halide (e.g. HF, HCl, HBr or HI), for example from, a hydro(halo)fluoroalkane, Thus the term “dehydrohalogenation” includes“dehydrofluorination”, “dehydrochlorination”, “dehydrobromination” and“dehydroiodination” of a hydro(halo)fluoroalkane.

The present invention provides a process for preparing a compound offormula CX₃(CX₂)_(n)CX═CX₂ or CX₃CX═CX(CX₂)_(n)CX₃ wherein each X is,independently, H or F provided that at least one X is F and n is 0, 1, 2or 3, which process comprises dehydrohalogenating a compound of formulaCX₃(CX₂)_(n)CXYCHX₂ or CX₃(CX₂)_(n)CXHCYX₂ or CX₃CXHCXY(CX₂)_(n)CX₃ orCX₃CXYCXH(CX₂)_(n)CX₃ wherein each X is, independently, H or F providedthat at least one X is F, n is 0, 1, 2 or 3 and Y is F, Cl, Br, or I, inthe presence of a zinc/chromia catalyst.

In some embodiments, a preferred feed for the process of the inventionis a mixed fluoro-chlorohexahalopropane or a hexafluoropropane.

Preferably, the compound of formula. CX₃(CX₂)_(n)CX═CX₂ isCF₃(CX₂)_(n)CF═CX₂. This compound, may be prepared bydehydrohalogenating a compound of formula CF₃(CX₂)_(n)CFYCHX₂ orCF₃(CX₂)_(n)CFHCYX₂.

More preferably, the compound of formula CX₃CX═CX(CX₂)_(n)CX₃ isCF₃CF═CH(CX₂)_(n)CX₃. This compound may be prepared bydehydrohalogenating a compound of formula CF₃CFHCHY(CX₂)_(n)CX₃ orCX₃CFYCH₂(CX₂)_(n)CX₃.

Preferably, n=0. The process is particularly suitable for preparing2,3,3,3-tetrafluoropropene (CF₃CF═CH₂, HFC-1234yf) or1,2,3,3,3-pentafluoropropene (CF₃CF═CHF, HFC-1225ye). In a particularlypreferred embodiment, the invention may be used for preparing HFC-1225yefrom either HFC-236ea or HFC-236cb, especially HFC-236ea.

CF₃CF═CH₂ and 1,3,3,3-tetrafluoropropene (CF₃CH═CHF) may be togetherprepared by the process of the invention. Alternatively, CF₃CF═CH₂ and1,2,3,3,3-pentafluoropropene (CF₃CF═CHF) may be together prepared by theprocess of the invention.

CF₃CF═CH₂ may be prepared by dehydrohalogenating a compound of formulaCF₃CFYCH₃ or CF₃CFHCYH₂.

The process of the invention is suitable for preparing any C₃₋₆(hydro)fluoroalkene by dehydrohalogenating (e.g. dehydrofluorinating ordehydrochlorinating) a C₃₋₆ hydro(halo)fluoroalkane. Optionally, theC₃₋₆ hydro(halo)fluoroalkane may first be fluorinated to a C₃₋₆hydrofluoroalkane which may then be dehydrofluorinated to a C₃₋₆(hydro)fluoroalkene.

Preferably, the C₃₋₆ (hydro)fluoroalkene is a (hydro)fluoropropeneprepared by the dehydrohalogenation of a hydro(halo)fluoropropane. Byway of example and for simplicity, unless otherwise stated, theremainder of the specification will describe the process of theinvention with reference to the preparation of (hydro)fluoropropenes.The skilled person will understand that such discussion is equallyapplicable to the preparation of (hydro)fluoro-butenes, pentenes andhexenes.

(Hydro)fluoropropenes prepared toy the process of the invention maycontain 0, 1, 2, 3, 4 or 5 hydrogen atoms and 1, 2, 3, 4, 5 or 6fluorine atoms. Preferred (hydro)fluoropropenes are those having from 3to 5 fluorine atoms (and thus from 1 to 3 hydrogen atoms), particularly4 or 5 fluorine atoms (and thus 1 or 2 hydrogen atoms). In other words,preferred (hydro)fluoropropenes are tetrafluoropropenes andpentafluoropropenes.

Examples of suitable tetrafluoropropenes include2,3,3,3-tetrafluoropropene (H₂C═CFCF₃), 1,3,3,3-tetrafluoropropene(HFC═CHCF₃), 1,2,3,3-tetrafluoropropene (HFC⊚CFCF₂H),1,1,3,3-tetrafluoropropene (F₂OCHCF₂H) and 1,1,2,3-tetrafluoropropene(F₂C═CFCH₂F). 1,3,3,3-tetrafluoropropene and 2,3,3,3-tetrafluoropropene(H₂C═CFCF₃) are preferred tetrafluoropropenes,2,3,3,3-tetrafluoropropene being particularly preferred. Unlessotherwise stated, this 2,3,3,3-tetrafluoropropene will be referred tohereinafter as HFC-1234yf and 1,3,3,3-tetrafluoropropene will bereferred to as HFC-1234ze.

Examples of suitable pentafluoropropenes include1,2,3,3,3-pentafluoropropene (HFC═CFCF₃), 1,1,3,3,3-pentafluoropropene(F₂C═CHCF₃) and 1,1,2,3,3-pentafluoropropene (F₂C═CFCF₂H). Of these,1,2,3,3,3-pentafluoropropene (HFC═CFCF₃) is preferred.

The (hydro)fluoropropenes which can be made by the process of theinvention may be prepared starting from one or more of a large number ofhydro(halo)fluoropropanes. Again, by way of example and for simplicity,unless otherwise stated, the remainder of the specification will bedescribed with reference to the preparation of HFC-1234yf.

HFC-1234yf may be prepared by a process comprising thedehydrofluorination of 1,1,1,2,2-pentafluoropropane (CH₃CF₂CF₃) or1,1,1,2,3-pentafluoropropane (CH₂FCHFCF₃). 1,1,1,2,2-pentafluoropropane,for example, may be prepared by fluorinating one or more of a largenumber of hydrochlorofluoropropanes including tetrafluorochloropropanessuch as 1,1,1,2-tetrafluoro-2-chloropropane and1,1,2,2-tetrafluoro-1-chloropropane, trifluorodichloropropanes such as1,1,1-trifluoro-2,2-dichloropropane, 1,1,2-trifluoro-1,2-dichloropropaneand 1,2,2-trifluoro-1,1-dichloropropane, difluorotrichloropropanes suchas 2,2-difluoro-1,1,1-trichloropropane,1,2-difluoro-1,1,2-trichloropropane and1,1-difluoro-1,2,2-trichloropropane and fluorotetrachloropropanes suchas 1-fluoro-1,1,2,2-tetrachloropropane and2-fluoro-1,1,1,2-tetrachloropropane, 1,1,1,2,2-pentafluoropropane (andthus ultimately HFC-1234yf) may also be prepared starting from1,1,1,2,2-pentachloropropane. In any of the abovehydrohalo(fluoro)propane precursors to 1,1,1,2,2-pentafluoropropane, oneor more of the chlorine substituents may be replaced by bromine oriodine.

Preferred hydro(halo)fluoropropanes for preparing HFC-1234yf include1,1,1,2,2-pentafluoropropane, 1,1,1,2-tetrafluoro-2-chloropropane and1,1,1-trifluoro-2,2-dichloropropane. It will be understood by theskilled person that 1,1,1-trifluoro-2,2-dichloropropane may befluorinated to give 1,1,1,2-tetrafluoro-2-chloropropane and/or1,1,1,2,2-pentafluoropropane. 1,1,1,2-tetrafluoro-2-chloropropane mayalso be fluorinated to produce 1,1,1,2,2-pentafluoropropane, which maythen be dehydrofluorinated to give HFC-1234yf.

Alternatively, 1,1,1,2-tetrafluoro-2-chloropropane may bedehydrochlorinated to give HFC-1234yf.

In a preferred aspect of the invention, it may be found that the processof the invention may be utilised to effect a degree of isomerisation ofthe (hydro)fluoroalkene of the invention. More specifically, andparticularly when the (hydro)fluoroalkene is R-1225ye, the effect of theresultant (hydro)fluoroalkene being in contact with the catalyst of theinvention may be to alter the ratio of E to Z isomers, thereby causingisomerisation.

In the particular context of R-1225ye, the effect is to increase theratio of Z isomer to the E isomer.

In a further aspect of the invention, there is provide a process forisomerising a C₃₋₆ (hydrohalo)fluoroalkene by contacting the C₃₋₆(hydrohalo)fluoroalkene with a catalyst. Also provided is the use of acatalyst for isomerising a C₃₋₆ (hydrohalo)fluoroalkene.

In a further aspect, there is provided, a process for isomerising a C₃₋₆(hydrohalo)fluoroalkene, the process comprising (i) contacting a E-C₃₋₆(hydrohalo)fluoroalkene with a catalyst to convert the E-C₃₋₆(hydrohalo)fluoroalkene to the C₃₋₆ Z-(hydrohalo)fluoroalkene.Conveniently, the C₃₋₆ Z-(hydrohalo)fluoroalkene can be recovered, ande.g. used in a subsequent procedure.

In a further aspect, the subject invention provides the use of acatalyst for isomerising a C₃₋₆ (hydrohalo)fluoroalkene, the usecomprising (i) contacting a E-C₃₋₆ (hydrohalo)fluoroalkene with acatalyst to convert the E-C₃₋₆ (hydrohalo)fluoroalkene to the Z-C₃₋₆(hydrohalo)fluoroalkene. Conveniently, the I-C₃₋₆(hydrohalo)fluoroalkene can be recovered, and e.g. used in a subsequentprocedure.

By “isomerisation” in this context is preferably meant changing theratio of the E and Z isomers (e.g. increasing the level of Z isomer)from what it was previously or, in particular in a situation where theisomerisation is carried out in situ, for instance as part of apreparation step for the (hydrohalo)fluoroalkene, changing the ratio ofE and Z isomers (e.g. increasing the level of Z isomer) compared to whatit would have been if the catalyst had not been utilised.

In a further aspect, the invention also provides an isomer blendproduced according to a process of the invention. The invention alsoprovides a refrigerant comprising an isomer blend produced according tothe process of the invention, and an automobile having an airconditioning system utilizing such an isomer blend.

Conveniently in an aspect of the invention, the invention may work bychanging the E/Z isomer ratio from that which is the kinematicdetermined mixture of isomers, from the reaction preparing the(hydrohalo)fluoroalkene.

In a further aspect of the invention, there is provided a process formaking a C₃₋₆ (hydrohalo)fluoroalkene composition comprising an enhancedlevel of Z isomer, conveniently a level of Z isomer enhanced beyond thelevel present when the C₃₋₆ (hydrohalo)fluoroalkene was formed, or thekinematic determined level of the Z isomer of the(hydrohalo)fluoroalkene, comprising the step of using a catalyst.Conveniently this aspect of the invention may comprise a clean up stepwhich enhances the level of Z isomer in such a composition.

In utilities where it is preferable to increase the level of the Zisomer in the blend, it is possible using the method of the invention toincrease the level of Z isomer by isomerising E isomer present in theblend to the Z isomer. The limit of how much E isomer can be convertedto Z isomer is determined by thermodynamic considerations.

The reaction pathways described above for producing HFC-1234-yf from1,1,1,2,2-pentafluoropropane, 1,1,1,2-tetrafluoro-2-chloropropane and1,1,1-trifluoro-2,2-dichloropropane are illustrated below.

In a further embodiment, HFC-1234yf may be prepared starting from1,1,1-trifluoro-2,3-dichloropropane, which can readily be prepared bychlorinating 1,1,1-trifluoromethylpropene. It is believed that there aretwo principal routes to HFC-1234 yf from1,1,1-trifluoro-2,3-dichloropropane, as illustrated below.

Route B proceeds via the fluorination (e.g. using HF, optionally in thepresence of a chromia-containing catalyst) of1,1,1-trifluoro-2,3-dichloropropane to give 1,1,1,2,3-pentafluoropropanewhich is then dehydrofluorinated to give HFC-1234yf. However, it isbelieved that route A may be favoured over route B.

Route A proceeds by dehydrochlorination of1,1,1-trifluoro-2,3-dichloropropane to give3,3,3-trifluoro-2-chloropropene which is then hydrofluorinated to give1,1,1,2-tetrafluoro-2-chloropropane. These two steps may be carried outin one pot by contacting 1,1,1-trifluoro-2,3-dichloropropane with HF inthe presence of a catalyst. However, it is believed that a two-stagereaction zone may be preferred, the first zone employing a relativelylow HF:organics ratio (e.g. from about 1:1 to about 5:1 ) to promote thedehydrochlorination and the second zone employing a relatively highHF:organics ratio (e.g. from about 5:1 to about 30:1) to promote thehydrofluorination. As described above,1,1,1,2-tetrafluoro-2-chloropropane may be fluorinated to pro du c e1,1,1,2,2-pentafluoropropane (e.g. using HF, optionally in the presenceof a chromia-containing catalyst), which may then be dehydrofluorinatedto give HFC-1234yf. Alternatively, 1,1,1,2-tetrafluoro-2-chloropropanemay be directly dehydrochlorinated to give HFC-1234yf.

1,1,1-trifluoro-2,3-dichloropropane is commercially available, but mayalso be prepared via a synthetic route starting from the cheapfeedstocks carbon tetrachloride (CCl₄) and ethylene. These two startingmaterials may be telomerised to produce 1,1,1,3-tetrachloropropane,which may then be fluorinated to produce 1,1,1,3-tetrafluoropropane(e.g. using HF, optionally in the presence of a chromia-containingcatalyst). Dehydrofluorination of 1,1,1,3-tetrafluoropropane (e.g. usingNaOH) would then produce 3,3,3-trifluoropropene, which may then bereadily chlorinated (e.g. with chlorine) to produce1,1,1-trifluoro-2,3-dichloropropane. This reaction scheme is summarisedbelow.

As mentioned above, 1,1,1,2,2-pentafluoropropane may be preparedstarting from 1,1,1,2,2-pentachloropropane. In this route (see below),1,1,1,2,2-pentachloropropane is fluorinated (e.g. using HF, optionallyin the presence of a chromia-containing catalyst) to produce1,1,1,2-tetrafluoro-2-chloropropane, which may also be fluorinated toproduce 1,1,1,2,2-pentafluoropropane followed by dehydrofluorination togive HFC-1234yf. Alternatively, 1,1,1,2-tetrafluoro-2-chloropropane maybe directly dehydrochlorinated to give HFC-1234yf.

1,1,1,2,2-pentachloropropane is a convenient intermediate in a route toHFC-1234yf starting from acetone. In such a synthetic route, acetone maybe chlorinated (for example using chlorine over a chromia catalyst) toproduce 1,1,1-trichloroacetone, which may be further chlorinated (forexample using PCl₅—see Advanced Organic Chemistry (Ed M B Smith and JMarch), Fifth Edition, page 1195) to produce1,1,1,2,2-pentachloropropane, as illustrated below.

Within the broad ambit of the invention, it has been found that thepreferred conditions for dehydrofluorination may depend on a number ofvariables, including the exact nature of the catalyst, and the pressureat which the reaction is carried out.

For instance, it has been found that the rate of fouling of the catalystmay be a function of the catalyst formulation. In general, the lower thelevel of zinc which was incorporated into the catalyst, the moreresistant the catalyst was to fouling; chromia catalyst containing nozinc was more resistant to fouling than chromia catalysts containingsome zinc. Further, when the process was carried out at atmosphericpressure, chromia catalysts were generally more resistant to foulingthan zinc/chromia catalysts.

However, chromia catalysts containing no zinc at all were moresusceptible to crystallisation under commercial production conditions.On a small scale, chromia catalysts of the type used in the exampleswere found to be stable in an inert atmosphere to temperatures around440° C., but this temperature was lower in oxidising atmospheres. It wasconsidered that it was likely that chromia. containing no zinc would,crystallise at operational temperatures, or at least during catalystregenerations. Crystallisation is highly exothermic, and veryproblematic in industrial scale production.

Additionally, high levels of conversion of 1,1,1,2,3,3-hexafluoropropene(HFC-236ea) to 1,2,3,3,3-pentafluoropropene (HFC-1225ye) were observedwhen the reaction was carried out at greater than about 300° C.

When the process is carried out at super-atmospheric pressure, differentcriteria apply. It was observed that at pressure, conversion rates ofHFC-236ea to HFC-1225ye were higher if the reaction were carried out inthe absence of an added HF flow. It was not possible to remove all HFfrom the reaction since HF is generated where HFC-236ea isdehydrofluorinated. However, a reduction in the HF level in the reactantstream resulted in higher conversion of HFC-236ea to HFC-1225ye,suggesting that (at least at pressure) the conversion is inhibited byHF, Further and surprisingly, if HF levels were reduced or removed fromthe reactant stream, the level of fouling observed on the catalyst wassurprisingly low. Operating the process of the invention at superatmospheric pressure may be desirable for various scale-up and generalprocessing reasons, allowing for example greater productivity fromapparatus of a given volume run at pressure.

The invention will now be illustrated, but not limited, by the followingExamples.

EXAMPLE 1 Dehydrofluorination of 1,1,1-trifluoro-2,3-dichloropropane

A 2 g sample of an amorphous catalyst composed of 6% Zn by weight onchromia was charged to a 15 cm×1.25 mm Inconnel reaction tube installedinside a tubular furnace. This catalyst was dried at 250° C. for 1 hourthen pre-fluorinated at an N₂:HF ratio of 6:1 for 1 hour at 250° C.before increasing the temperature to 380° C. at which point the nitrogendiluent flow was stopped. After approximately 18 hours, the HF feed wasswitched off and the reactor was cooled to 200° C.

The organic feed (comprising 1,1,1-trifluoro-2,3-dichloropropane) and HFwere then passed over the catalyst with a contact time of 5 seconds at areaction temperature of from 180 to 380° C. (varied at 20° C. intervals)and a pressure of 1 bara using either an HF:organics ratio of 15:1 or5:1. At each temperature, the system was allowed to equilibrate forabout 20 minutes before reactor off-gas samples were taken at eachtemperature for analysis by either GC or GC-MS. The reaction productscould be resolved using a Plot Silica column with temperatureprogramming (at about 40-200° C. at 5° C./min). The GC method wascalibrated using the available standards (principally the feed andproduct) and an average of these was used to quantify those componentsidentified but for which standards were not available and any unknowns.

The results of the temperature scans at the two different HF:organicsratios are presented in Tables 1 and 2 and FIGS. 1 and 2.

TABLE 1 Dehydrofluorination of CF₃CHClCH₂Cl at an HF:organics ratio of15:1 Compound Reaction temperature (° C.) (mol %) 180 200 220 240 260280 300 320 340 360 380 CF₃CF═CH₂ 0.0 0.0 0.3 2.6 4.9 7.9 15.3 25.4 37.641.1 0.0 CF₃CF₂CH₃ 0.0 0.0 0.0 0.4 3.1 5.0 5.6 5.2 4.3 2.4 0.0CF₃CCl═CH₂ 4.0 13.3 41.1 79.1 90.3 85.9 78.1 67.7 53.8 42.5 4.0 orCF₃CH═CHCl Unknown 0.4 2.8 9.4 7.2 0.2 0.0 0.0 0.0 0.0 0.0 0.4 Unknown16.8 22.0 10.3 1.6 0.0 0.0 0.0 0.0 0.0 0.0 16.8 CF₃CHClCH₂Cl 78.4 61.136.5 6.6 0.2 0.1 0.0 0.0 0.0 0.0 78.4

TABLE 2 Dehydrofluorination of CF₃CHClCH₂Cl at an HF:organics ratio of5:1 Compound Reaction temperature (° C.) (mol %) 180 200 220 240 260 280300 320 340 360 380 CF₃CF═CH₂ — 0.0 0.2 1.0 2.1 3.4 6.2 11.7 17.7 23.123.4 CF₃CF₂CH₃ — 0.0 0.0 0.2 0.8 2.0 2.6 2.8 2.5 1.5 1.1 CF₃CCl═CH₂ —16.4 47.7 80.6 93.8 93.5 89.8 83.6 76.3 68.3 60.7 or CF₃CH═CHCl Unknown— 2.0 5.5 4.5 0.8 0.1 0.0 0.0 0.0 0.0 0.0 Unknown — 14.3 5.4 1.1 0.1 0.00.0 0.0 0.0 0.0 0.0 CF₃CHClCH₂Cl — 66.6 39.6 10.9 1.2 0.0 0.0 0.0 0.00.0 0.0

Turning first to the data obtained using the HF:organics ratio of 15:1(Table 1 and FIG. 1), the feed level of CF₃CHClCH₂Cl dropped fairlyrapidly as the temperature increased and conversion appeared completearound 280° C. As the feed, level dropped the species identified asCF₃CCl═CH₂ increased, indicating it to be the primary reaction product,formed by elimination of HCl. It is believed that the next step washydrofluorination of CF₃CCl═CH₂ to give CF₃CFClCH₃, HFC-1234yf could beformed from CF₃CFClCH₃ directly by dehydrochlorination or indirectly viafluorination to give CF₃CF₂CH₃ followed, by dehydrofluorination.

This reaction mechanism requires both addition and elimination ofhydrogen halides and therefore the outcome is likely to be verysensitive to HF:organics ratio. The experiments at lower ratiodemonstrated this to be the case.

Regarding the data obtained using the HF:organics ratio of 5:1 (Table 2and FIG. 2), complete conversion of the feed and peak concentration ofCF₃CCl═CH₂ was observed at 260° C. and the final yields of HFC-1234yfwere lower compared to the experiment with the higher HF:organics ratio.Without being bound by theory, it is believed that the onward, reaction,of CF₃CCl═CH₂, necessary to form the desired product, is favoured athigher HF:organics ratios but its initial formation is favoured at lowerHF:organics ratios, indicating that a two-stage reaction zone might bepreferred.

EXAMPLE 2 Dehydrofluorination of 1,1,1,2,2-pentafluoropropane

A 2 g sample of an amorphous catalyst composed of 6% Zn by weight onchromia was charged to a 15 cm×1.25 mm Inconel reaction tube installedinside a tubular furnace. This catalyst was dried at 250° C. for 1 hourthen pre-fluorinated at an N₂:HF ratio of 6:1 for 1 hour at 250° C.before increasing the temperature to 380° C. at which point the nitrogendiluent flow was stopped. After approximately 18 hours, the HF feed wasswitched off and the reactor was cooled to 200° C.

The organic feed (comprising 1,1,1,2,2-pentafluoropropane) and HF wasthen passed over the catalyst with a contact time of 5 seconds at areaction temperature of from 180 to 380° C. (varied at 20° C. intervals)and a pressure of 1 bara using either an HF:organics ratio of 15:1 or5:1. At each temperature, the system was allowed to equilibrate forabout 20 minutes before reactor off-gas samples were taken at eachtemperature for analysis by either GC or GC-MS as described above forExample 1 and the results are illustrated in Table 3 and FIG. 3. Theseresults show that 1,1,1,2,2-pentafluoropropane was dehydrofluorinated toHFC-1234yf at high selectivity at about 300° C.

TABLE 3 Dehydrofluorination of CF₃CF₂CH₃ at and HF:organics ratio of 5:1Compound Reaction temperature (° C.) (mol %) 200 220 240 260 280 300 320340 360 380 400 CF₃CF═CH₂ 0.1 0.6 3.6 15.1 46.9 74.2 85.5 88.1 66.0 48.40.1 CF₃CF₂CH₃ 99.4 98.7 95.9 84.5 52.6 25.0 13.0 7.5 3.6 0.7 99.4Unknown 0.1 0.2 0.3 0.4 0.4 0.7 0.9 1.5 5.2 8.2 0.1 Unknown 0.2 0.1 0.00.0 0.0 0.0 0.0 0.0 0.0 0.0 0.2

EXAMPLE 3 Dehydrofluorination of 1,1,1,2,2,3-hexafluoropropane(HFC-236cb) and 1,1,1,2,3,3-hexafluoropropane (HFC-236ea) with HF

A 2 g sample of an amorphous catalyst composed of 6% Zn by weight onchromia was charged to a 15 cm×1.25 mm Inconel reaction tube installedinside a tubular furnace. This catalyst was dried at 250° C. for 1 hourthen pre-fluorinated at an N₂:HF ratio of 6:1 for 1 hour at 250° C.before increasing the temperature to 380° C. at which point the nitrogendiluent flow was stopped. After approximately 18 hours, the HF feed wasswitched off and the reactor was cooled to 220-240° C.

Following pre-fluorination, the dehydrofluorination of either HFC-236eaor HFC-236cb was studied as a function of temperature and HF:236 ratio.Feed gas flow rates were chosen so that a contact time of c.a. 5 secondswas achieved between the catalyst and feed mixture. HF:236 ratios wereexplored in the range 0-10. At each temperature, the system was allowedto equilibrate for about 20 minutes before reactor off-gas samples weretaken at each temperature for analysis by either GC or GC-MS asdescribed above for Example 1 and the results are illustrated in Tables4 and 5 and FIGS. 4 and 5.

TABLE 4 Dehydrofluorination of HFC-236ea at varying HF:organics ratios236ea Z- E- Temperature Ratio Conversion 1225ye 1225ye Selectavity (°C.) HF:236ea (%) (%) (%) (Z + E %) 240.0 0.0 26.5 24.0 2.2 99.1 260.00.0 42.9 38.2 4.2 98.8 280.0 0.0 75.8 65.9 7.9 97.4 300.0 0.0 89.3 77.010.3 97.7 320.0 0.0 94.7 80.2 12.1 97.5 240.0 2.5 3.0 0.1 0.0 2.7 260.02.5 2.8 0.5 0.1 19.6 280.0 2.5 5.4 3.2 0.4 66.7 300.0 2.5 21.2 17.1 2.190.7 320.0 2.5 56.1 46.8 6.6 95.3 340.0 2.5 82.2 67.6 10.6 95.2 360.02.5 90.0 72.2 11.8 93.4 380.0 2.5 94.0 73.7 12.6 91.8 240.0 5.0 2.5 0.00.0 0.8 260.0 5.0 2.3 0.2 0.0 7.7 280.0 5.0 2.4 0.8 0.1 38.5 300.0 5.08.2 4.6 0.6 63.2 320.0 5.0 23.4 18.0 2.7 88.1 340.0 5.0 80.0 63.1 9.590.8 360.0 5.0 90.4 65.8 10.5 84.4 380.0 5.0 95.9 49.2 8.0 59.6 240.010.0 0.4 0.1 0.0 40.5 260.0 10.0 1.2 1.0 0.1 93.4 280.0 10.0 5.4 4.1 0.685.9 300.0 10.0 15.2 13.1 1.6 96.6 320.0 10.0 56.1 47.7 6.5 96.7 340.010.0 86.3 70.8 10.8 94.6 360.0 10.0 91.3 72.8 11.4 92.1 380.0 10.0 95.773.0 12.5 89.5

TABLE 5 Dehydrofluorination of HFC-236cb at varying HF:organics ratios236cb Z- E- Temperature Ratio Conversion 1225ye 1225ye Selectivity (°C.) HF:236cb (%) (%) (%) (Z + E %) 240.0 0.0 5.0 3.8 0.4 83.2 260.0 0.020.6 16.2 2.2 89.7 280.0 0.0 20.6 17.4 2.1 94.3 300.0 0.0 47.3 39.5 5.194.3 320.0 0.0 76.7 63.4 9.1 94.6 340.0 0.0 93.6 77.4 11.2 94.6 360.00.0 97.6 78.5 12.3 93.0 240.0 2.5 0.3 0.0 0.0 0.0 260.0 2.5 0.3 0.0 0.04.8 280.0 2.5 0.3 0.1 0.0 23.8 300.0 2.5 0.6 0.4 0.0 69.7 320.0 2.5 1.81.3 0.2 82.8 340.0 2.5 6.1 4.5 0.7 84.7 360.0 2.5 61.6 46.2 7.3 86.9380.0 2.5 90.8 69.0 11.8 88.9 400.0 5.0 96.7 70.2 12.8 85.8 240.0 5.00.0 0.0 0.0 0.0 260.0 5.0 0.4 0.0 0.0 0.0 280.0 5.0 0.2 0.1 0.0 54.2300.0 5.0 0.5 0.4 0.1 81.5 320.0 5.0 4.5 1.5 0.3 39.3 340.0 5.0 9.0 6.21.0 79.7 360.0 5.0 77.4 55.9 9.0 83.8 380.0 5.0 95.6 67.1 11.3 81.9400.0 5.0 98.2 61.2 10.9 73.4 240.0 10.0 0.3 0.0 0.0 7.1 260.0 10.0 0.30.1 0.0 26.5 280.0 10.0 0.8 0.4 0.1 55.6 300.0 10.0 2.3 1.3 0.2 61.7320.0 10.0 5.7 4.1 0.6 84.1 340.0 10.0 21.6 14.8 2.4 79.2 360.0 10.091.6 64.3 10.9 82.2 380.0 10.0 96.2 59.8 10.2 72.8

The results show that both HFC-236ea and HFC-236cb can be used toprepare 3,3,3,2,1-pentafluoropropene (HFC-1225ye) bydehydrofluorination, but that HFC-236ea was generally more susceptibleto dehydrofluorination than HFC-236cb under the conditions employed. TheZ isomer of EFC-1225ye was predominantly formed, although significantquantities of the E isomer were also formed. The presence of HF stronglydepresses the dehydrofluorination reaction.

EXAMPLE 4

In the ensuing Examples 4 to 6, the following general protocol applied.

A reactor tube was charged with 2 g catalyst, which was dried at 250° C.under nitrogen (65 ml/min) for 2 hours. The catalyst was thenpre-fluorinated with HF (30 ml/min) and nitrogen (65 ml/min) for 1 hourat 250° C. The temperature was then ramped to 460° C. and thepre-fluorination continued under neat HF (30 ml/min) overnight. Feedrates and temperatures were then set so as to achieve the desiredreactor conditions and the reactor off-gases sampled at an appropriatefrequency using an automated system. HF was fed using a nitrogen spargeand so some dilution of the feed mixture with inerts was unavoidable.

When regeneration of the catalyst was necessary, the organic feed wasswitched off and the HF flow set to 6 ml/min and a mixture of air (3ml/min) and nitrogen (60 ml/min) passed over the catalyst at 380° C.overnight.

In the Example itself, the reactor was charged with a 6% zinc/chromiacatalyst. Following pre-fluorination the reactor was cooled to 340° C.and a reaction mixture consisting of HF (6 ml/min), HFC-236ea (1 ml/min)and nitrogen (5 ml/min) passed over it. Reactor off-gas (ROG) sampleswere regularly taken in order to monitor catalyst performance. When thecatalyst performance was deemed to have dropped too far, the catalystwas regenerated as described, above and the experiment repeated. A totalof 3 such cycles were completed. HFC-1225ye Z yield data from theseexperiments is plotted in FIG. 6.

These experiments indicated that organic fouling of the catalystoccurred in use and was responsible for the observed loss inperformance. Furthermore, the process could be completely reversed by anoxidative regeneration.

EXAMPLE 5

The following example demonstrates the impact of the HF:organic ratio oncatalyst fouling rates.

The reactor was charged with a composite

comprising a 6% zinc/chromia catalyst. In the first cycle followingpre-fluorination the fouling rate was determined at an HF: HFC-236earatio of 3:1. In the second cycle following a standard regeneration thefouling rate was measured at a ratio of 6:1 and in the final cycle inthis sequence it was re-measured at a ratio of 1.5:1. In theseexperiments the partial pressure of HF was constant at 0.5 bara and thecontact time constant at 4.4 seconds. The Z-HFC-1225ye yield vs time forthis sequence of experiments is plotted, in FIG. 7. There did not appearto be any relationship between ratio and yield. At ratios between 3:1and 6:1 the fouling rates appeared similar, but did look to increase at1.5:1.

EXAMPLE 6

The following example demonstrates the impact of catalyst formulation onfouling rates and yield, of HFC-1225ye.

The relative performance of a 0% Zn/chromia, 6% Zn/chromia and 10% Znchromia were determined using the methodology described above. Thereaction temperature, ratio and contact times were all constant at 340°C., 6:1 and 4.4 seconds respectively over the sequence of experiments.The results are summarized in FIG. 8. The effect of Zn loading onperformance and stability was quite marked. The initial performance ofthe 0% and 6% Zn catalysts was similar but the performance of the 10%catalyst was relatively poor. In terms of fouling rates it was alsoclear that the 0% Zn catalyst was the most stable.

EXAMPLE 7

A sample of a chromia catalyst containing no zinc was analysed usingdifferential scanning calorimentry (DSC) techniques under nitrogen andair atmospheres. The results are shown in FIG. 9.

The results show that in an inert atmosphere the chromia was stable toabout 440° C., but that this was reduced under an oxidising atmosphere.From this it can be concluded that a chromia catalyst containing no zinccould crystallise in use, or at least during regenerations.

EXAMPLE 8

In a slight modification to Example 4, a reactor tube was prepared asoutlined in the general protocol outlined in Example 4 and the feedrates were set at HF=6 ml/minute, HFC-236ea=2 ml/minute, nitrogen=4ml/minute over a scan of temperature, on a series of different catalystsshown in Table 6. This example was conducted at atmospheric pressure.

TABLE 6 Catalyst screening temperature scan results ° C. 200 215 230 245260 275 290 305 320 335 350 365 380 395 410 425 440 455 470 485 500Empty reactor tube HFD- — — 0.7 0.3 0.2  0.2  0.1  0.1  0.2  0.2  0.3 0.5  0.8  1.2  1.8  2.2  2.6 2.8 2.8 2.9 — 1225ye yield Pure chromiaHFC- 0.1 0.1 0.3 0.2 0.3 15.5 34.5 52.6 60.4 65.1 68.8 71.2 73.9 73.973.2 73.3 74.2 — — — — 1225ye yield 0.5% Zn/chromia HFC- 0.0 0.1 0.3 0.40.4  9.9 30.1 51.5 61.0 66.0 69.3 71.6 73.8 74.3 73.8 73.6 — — — — —1225ye yield 6% Zn/chromia HFC- 0.0 0.1 0.2 0.4 0.5  0.5 11.2 27.1 49.563.9 69.9 72.7 74.0 74.3 74.7 — — — — — — 1225ye yield 10% Zn/chromiaHFC- 0.0 0.0 0.1 0.3 0.5  4.5 15.4 31.5 49.6 61.1 68.9 71.0 74.4 74.174.8 74.6 — — — — — 1225ye yield

The results show that the conversion of HFC-236ea to HFC-1225ye is acatalytic one and not merely a thermal decomposition, based on the verypoor yield obtained when using an empty tube.

Comparing yields between at between 260° C. and 305° C., chromiacontaining no zinc produces the highest conversion. At a temperatureabove 305° C., the conversion of all of catalysts tested is generallysimilar. It was also found that the fouling resistance decreased as thezinc loading increased. However, the apparent preferred performance ofchromia catalysts containing no zinc should be balanced against thecrystallisation tendency of pure chromia catalysts at scale.

EXAMPLE 9

In the ensuing experiments conducted at increased pressure the followinggeneral protocol applied.

Unless specified otherwise, the catalyst employed was a 6 wt %zinc/chromia catalyst which was charged to the rig. The catalyst wasdried overnight in a stream of nitrogen (80 ml/min at 3 barg) and thenprefluorinated in stages. In stage 1 the temperature was raised to 300°C. and the catalyst was contacted with dilute HF (4 ml/min+80 ml/minnitrogen at 3 barg). This treatment was continued overnight and then thenitrogen flow was switched off and the temperature maintained at 300° C.for a further 4 hours. After this period the temperature was ramped to380° C. at 25° C./hr. These conditions were maintained for a further 7hours. The HFC-23 6ea→HFC E/Z-1225ye reaction was then studied under arange of conditions.

In this example and Example 10, the conversion rate in the process ofthe invention when conducted at pressure is apparent, together with thebenefit of omitting HF from the reactant flow.

Following pre-fluorination, the HF and HFC-236ea feed flows were set toapproximately 90 and 30 m ml/min (at STP) respectively, and the impactof temperature on conversion studied at 5 barg and 10 barg. The resultsare summarized in FIG. 7.

TABLE 7 HEC-236ea→HFC-1225ye reaction at 3 HF:1 HFC- 236ea HFC-236eaTemperature (° C.) Pressure (Barg) conversion (mol %) 330 5 3.8079 350 53.7452 350 5 3.8359 370 5 3.8090 315 10 2.6044 330 10 5.1410 330 104.3250 350 10 8.6508 350 10 6.0846 330 5 3.5644 330 5 4.2492 350 53.9889 350 5 3.4571

The catalyst was given an HF:air regeneration (15:1) at 380° C. and someof the data points at 5 barg operation repeated; these are also shown inFIG. 10.

EXAMPLE 10

Following on from Example 9, the experiment was repeated but with noco-fed HF. The resultant HFC-236ea conversion shown in Table 8.

TABLE 8 HFC-236ea→HFC-1225-ye reaction without co-fed HF HEC-236eaTemperature (° C.) Pressure (Barg) conversion (mol %) 330 5 46.7366 3305 45.7122 340 5 52.8137 340 5 51.9489 340 5 52.0404 350 5 56.8593 350 557.5889

In the absence of HF there is a marked increase in catalyst performance,with higher conversion rates observed.

To further demonstrate the adverse effects that HF was causing, the feedwas diluted with inert diluent nitrogen, with the effect measured in asingle pass conversion at 340° C. The results are shown in Table 9.

TABLE 9 Impact of feed dilution on HFC-236ea→HFC- 1225ye at 5 bargTemper- HFC-236ea Contact HFC-236ea HFC-236ea ature feed Nitrogen timemole conversion (° C.) (ml/min) (ml/min) (sec) fraction (%) 340 33.32 037.70 1.00 48.82 340 22.41 0 56.06 1.00 49.11 340 27.06 0 46.43 1.0051.18 340 30.67 20 24.80 0.61 57.41 340 17.17 20 33.80 0.46 58.29 34021.73 20 30.11 0.52 65.93 340 25.94 20 27.35 0.56 56.35 340 18.77 2032.41 0.48 57.10 340 23.20 40 19.88 0.37 63.12 340 25.45 40 19.20 0.3961.77 340 26.55 60 14.52 0.31 64.70 340 17.60 60 16.19 0.23 65.52 34012.90 80 13.52 0.14 74.61 340 11.94 80 13.67 0.13 68.38

As the feed is diluted, the conversion rose even though the contact timeis reducing.

EXAMPLE 11

This example demonstrates the lower than expected levels of catalystfouling which were found to occur when the conversion of HFC-236ea toHFC-1226ye was carried out at pressure in the absence of HF. Thecatalyst was regenerated as described above in the context of Example 9but substituting nitrogen for HF, and then “neat” HFC-236ea at a rate ofapproximately 20 ml/minute was passed over it at 340° C. and 5 barg. Thecatalyst performance was monitored, and the results are shown in Table10.

TABLE 10 HFC-236ea→HFC-1225ye coking study at 340° C. and 5 barg in theabsence of co-fed HF Normalised mole % Temper- 236ee Time ature 236ea CTZ- E- conversion (hrs) (° C.) (ml/min) (sec) 1234yf 1225zc 1225ye 1225ye227ea 236cb 236ee (%) 0.0 340 2.89 435.44 0.15 0.00 57.60 7.49 1.37 7.0726.17 73.83 0.3 340 26.92 46.67 0.19 0.00 43.86 5.96 0.41 4.35 45.0154.99 1.8 340 19.75 63.61 0.20 0.00 43.84 5.97 0.27 3.70 45.83 54.17 2.6340 28.23 44.51 0.20 0.00 43.69 5.94 0.26 3.82 45.92 54.08 3.6 340 22.6755.42 0.21 0.00 43.73 5.94 0.25 3.97 45.77 54.23 4.4 340 22.77 55.170.20 0.00 43.91 6.02 0.22 3.42 46.10 53.90 5.0 340 27.46 45.76 0.21 0.0044.05 6.01 0.22 3.31 46.08 53.92 21.6 340 19.26 65.22 0.21 0.00 43.846.00 0.18 3.34 46.30 53.70 23.1 340 13.66 91.97 0.20 0.00 43.91 5.940.18 3.64 45.99 54.01 23.8 340 21.62 58.10 0.21 0.00 43.73 5.95 0.183.24 46.55 53.45 25.6 340 31 .11 40.39 0.22 0.00 43.48 5.99 0.19 3.0446.96 53.04 26.4 340 21.06 59.67 0.21 0.00 43.74 5.95 0.19 2.91 46.8753.13 27.6 340 31.31 40.13 0.21 0.00 43.72 6.00 0.18 3.08 46.67 53.3328.3 340 22.32 56.29 0.20 0.00 43.62 5.94 0.18 3.36 46.56 53.44 29.6 34020.19 62.23 0.22 0.00 44.37 6.11 0.18 2.83 46.16 53.84 30.4 340 24.6151.06 0.23 0.00 44.21 6.13 0.19 2.84 46.27 53.73 31.5 340 24.69 50.880.21 0.00 43.96 6.09 0.18 3.57 45.85 54.15 32.8 340 15.03 83.58 0.210.00 43.97 6.03 0.18 3.04 46.42 53.58 34.3 340 14.53 86.48 0.21 0.0044.47 6.08 0.18 3.20 45.70 54.30 36.1 340 19.60 64.11 0.22 0.00 44.046.05 0.19 3.03 46.45 53.55 52.8 340 22.87 54.94 0.23 0.00 44.15 6.180.18 2.24 46.89 53.11 54.3 340 23.27 53.99 0.23 0.00 43.82 6.07 0.182.24 47.34 52.66 56.9 340 22.48 55.90 0.22 0.00 43.83 6.07 0.18 2.3347.23 52.77 58.8 340 20.36 61.70 0.22 0.00 43.86 6.07 0.18 2.57 46.9653.04 60.0 340 19.50 64.44 0.22 0.00 44.16 6.11 0.18 2.38 46.82 53.1876.6 340 21.11 59.51 0.23 0.00 44.14 6.20 0.18 1.96 47.16 52.84 78.6 34022.90 54.86 0.23 0.00 43.95 6.19 0.18 2.00 47.33 52.67 80.6 340 26.2947.80 0.23 0.00 43.87 6.16 0.18 1.97 47.47 52.53 81.8 340 21.51 58.410.23 0.00 43.42 6.11 0.18 1.71 48.22 51.78 83.6 340 22.41 56.06 0.220.00 44.11 6.13 0.18 2.55 46.69 53.31 100.8 340 29.37 42.78 0.23 0.0043.52 6.16 0.18 1.66 48.13 51.87 101.8 340 13.36 94.05 0.23 0.00 43.966.16 0.18 1.74 47.59 52.41 103.3 340 23.20 54.16 0.22 0.00 43.61 6.150.18 2.40 47.30 52.70 104.9 340 22.83 55.05 0.22 0.00 43.33 6.02 0.182.02 48.09 51.91 106.5 340 16.79 74.81 0.22 0.00 43.75 6.20 0.18 2.2347.29 52.71 108.2 340 17.36 72.37 0.23 0.00 44.11 6.17 0.18 1.92 47.2652.74 124.6 340 19.78 63.51 0.23 0.00 43.78 6.22 0.18 1.62 47.84 52.16125.9 340 27.77 45.25 0.23 0.00 43.53 6.18 0.18 1.51 48.23 51.77 127.3340 19.68 63.83 0.22 0.00 44.07 6.19 0.18 2.00 47.22 52.78 128.8 34022.98 54.68 0.23 0.00 42.82 6.03 0.18 1.27 49.34 50.66 130.1 340 25.1250.01 0.23 0.00 43.25 6.14 0.18 1.39 48.68 51.32

Surprisingly, the catalyst performance was good and steady over a periodof 120 hours, with no indication of fouling. The experiment was repeatedat 10 barg; the results are shown in Table 11.

TABLE 11 HFC-236ea→HFC-1225ye coking study at 340° C. and 10 barg in theabsence of co-fed HF Normalised mol % N2 Contact 236ea Time Temp 236eaDiluent time Z- E- conv (hrs) (° C.) (ml/min) (ml/min) (sec) 1234yf1225zc 1225ye 1225ye 227ea 236cb 236ee (%) 0.42 340 11.44 0 201.30 0.160.01 42.71 5.60 0.94 8.44 41.94 58.06 1.00 340 18.02 0 127.84 0.16 0.0034.62 4.67 0.58 6.32 53.30 46.70 2.00 340 14.83 0 155.27 0.16 0.00 34.324.73 0.37 5.85 54.40 45.60 3.00 340 17.56 0 131.16 0.16 0.00 34.14 4.720.34 5.50 54.87 45.13 4.33 340 18.31 0 125.82 0.16 0.00 34.30 4.72 0.325.25 54.98 45.02 5.33 340 11.85 0 194.41 0.17 0.00 34.43 4.72 0.31 5.0155.20 44.80 22.00 340 22.35 0 103.05 0.18 0.00 34.40 4.81 0.25 3.5256.69 43.31 23.17 340 15.13 0 152.25 0.17 0.00 34.30 4.81 0.25 3.4756.83 43.17 24.25 340 9.41 0 244.82 0.17 0.00 34.28 4.76 0.25 3.66 56.7243.28 25.33 340 19.27 0 119.55 0.17 0.00 34.23 4.79 0.25 3.61 56.7743.23 25.83 340 17.59 0 130.93 0.17 0.00 34.18 4.77 0.25 3.68 56.7743.23 43.33 340 19.63 0 117.37 0.17 0.00 34.44 4.85 0.24 2.99 57.1342.87 44.25 340 21.35 0 107.90 0.18 0.00 34.30 4.80 0.24 2.89 57.4042.60 44.83 340 6.81 40 49.20 0.24 0.00 48.89 6.78 0.16 2.33 41.46 58.5445.67 340 19.86 40 38.48 0.25 0.00 49.22 6.91 0.15 2.44 40.89 59.1146.50 340 19.31 40 38.84 0.25 0.00 49.66 6.95 0.15 2.49 40.36 59.6447.08 340 20.01 40 38.38 0.25 0.00 49.84 6.96 0.15 2.52 40.14 59.8647.67 340 18.11 80 23.48 0.29 0.00 57.01 8.00 0.11 2.24 32.23 67.7748.17 340 13.42 80 24.66 0.29 0.00 57.83 8.08 0.11 2.19 31.39 68.6149.08 340 14.09 80 24.48 0.29 0.00 58.00 8.10 0.11 2.22 31.16 68.8449.75 340 9.15 80 25.84 0.28 0.00 58.19 8.09 0.11 2.19 31.02 68.98 50.33340 15.74 80 24.06 0.29 0.00 57.91 8.10 0.10 2.20 31.27 68.73 67.00 34015.51 80 24.12 0.29 0.00 56.89 8.01 0.11 1.85 32.73 67.27 68.00 34016.00 120 16.94 0.31 0.00 61.18 8.69 0.08 1.70 27.92 72.08 68.50 34016.84 120 16.83 0.31 0.00 61.36 8.70 0.08 1.68 27.76 72.24 69.25 34017.19 120 16.79 0.31 0.00 61.25 8.66 0.08 1.69 27.90 72.10 71.00 3408.67 120 17.90 0.32 0.00 62.48 8.73 0.08 1.62 26.67 73.33 71.75 340 6.65160 13.82 0.32 0.00 64.92 9.09 0.07 1.47 24.04 75.96 72.42 340 16.04 16013.08 0.32 0.00 64.25 9.10 0.07 1.51 24.65 75.35 73.42 340 1.08 16014.30 0.31 0.00 65.22 9.07 0.07 1.49 23.76 76.24 73.75 340 14.16 8024.46 0.29 0.00 57.90 8.13 0.10 1.81 31.64 68.36 74.25 340 13.86 8024.54 0.29 0.00 57.85 8.11 0.10 1.75 31.76 68.24 90.83 340 12.41 8024.93 0.30 0.00 56.63 7.96 0.11 1.55 33.34 66.66 91.50 340 17.07 8023.73 0.30 0.00 55.51 7.85 0.11 1.48 34.63 65.37 92.17 340 14.69 8024.33 0.30 0.00 54.69 7.75 0.12 1.34 35.68 64.32 93.00 340 19.05 8023.26 0.29 0.00 54.76 7.80 0.12 1.40 35.53 64.47 93.75 340 24.15 8022.12 0.29 0.00 53.91 7.71 0.12 1.39 36.46 63.54 95.17 340 21.02 8022.80 0.29 0.00 54.49 7.73 0.12 1.38 35.88 64.12 96.00 340 21.25 8022.75 0.29 0.00 52.93 7.57 0.12 1.27 37.70 62.30 97.17 340 15.94 8024.01 0.29 0.00 53.70 7.63 0.12 1.26 36.87 63.13

At the higher pressure, the conversion rate was somewhat lower, againreflecting the HF inhibition. The impact after feed dilution can be seenafter 44.25 hours, when nitrogen was added to the HFC-236ea feed. Againover the course of the whole experiment there was little sign ofcatalyst fouling.

EXAMPLE 12

This example demonstrates the beneficial effect

of diluting the feed (e.g. HFC-236ea) during catalytic conversion atpressure with a recycled material in the context of the process, e.g. anE/Z isomer mix of the resultant HFC-1225ye product, or an isomer richblend of HFC-1225ye (by isomer rich is meant a blend of E and Z isomerswhich differs from that which had been normally produced as a result ofthe process. The isomer rich blend could for example comprise a blend ofE and Z isomers which contains a higher level of either E or Z isomerthan would normally be thermodynamically formed, or it could containeither pure E isomer or pure Z isomer, conveniently pure Z isomer).

In the example, HFC-236ea feed was diluted with Z-HFC-1225ye in theratio 30:70. The blend was passed over freshly regenerated catalyst at340° C. and 10 barg. The results are summarised in Table 12.

TABLE 12 HFC-236ea→HFC-1225ye coking study at 340° C. and 10 barg in theabsence of co-fed HF using EFC-1225ye as a diluent Normalised mole %Total 236ea Time Temp orgs 1225ye 236ea CT Z- E- conv (hrs) (° C.)(ml/min) (ml/min) (ml/min) (sec) 1234yf 1225zc 1225ye 1225ye 227ea 236cb236ee (%) 18.75 340 32.20 22.54 9.66 71.53 0.06 0.20 65.41 9.00 0.025.66 19.29 35.71 19.33 340 30.24 21.17 9.07 76.17 0.06 0.20 65.66 8.980.02 5.51 19.20 35.99 20.25 340 32.09 22.46 9.63 71.78 0.06 0.20 65.488.95 0.02 5.47 19.37 35.42 21.25 340 33.40 23.38 10.02 68.97 0.06 0.2165.79 9.01 0.02 5.39 19.10 36.32 22.92 340 26.94 18.86 8.08 85.51 0.060.20 65.88 8.95 0.03 5.44 19.02 36.61 24.92 340 30.88 21.62 9.26 74.590.06 0.20 65.43 9.00 0.03 5.55 19.28 35.73 25.92 340 19.02 13.31 5.71121.11 0.06 0.21 66.19 8.96 0.03 5.37 18.79 37.36 42.58 340 21.40 14.986.42 107.61 0.06 0.20 66.07 9.04 0.03 5.12 19.02 36.61 43.25 340 22.1015.47 6.63 104.24 0.06 0.20 65.69 8.96 0.03 5.06 19.53 34.91 44.17 34022.53 15.77 6.76 102.25 0.06 0.20 65.93 9.00 0.03 4.95 19.33 35.56 45.75340 25.76 18.03 7.73 89.42 0.06 0.21 66.14 9.08 0.03 5.03 19.03 36.5749.58 340 24.29 17.00 7.29 94.82 0.06 0.20 65.52 9.01 0.04 5.05 19.6134.63 67.25 340 23.16 16.21 6.95 99.48 0.07 0.20 65.55 9.04 0.03 4.3420.27 32.44 68.67 340 16.73 11.71 5.02 137.67 0.06 0.22 67.33 9.11 0.044.01 18.77 37.44 69.58 340 20.52 14.36 6.16 112.25 0.06 0.21 66.19 9.080.04 4.54 19.38 35.39 71.00 340 15.58 10.91 4.67 147.86 0.06 0.21 66.359.09 0.04 4.51 19.24 35.87 72.00 340 22.78 15.94 6.83 101.14 0.07 0.2166.09 9.07 0.04 4.36 19.67 34.44 73.33 340 16.16 11.31 4.85 142.53 0.070.21 66.48 9.03 0.03 4.24 19.45 35.16 90.75 340 21.73 15.21 6.52 106.000.06 0.20 66.00 9.05 0.04 4.11 19.96 33.45 92.00 340 16.34 11.44 4.90140.94 0.07 0.20 66.27 9.04 0.03 3.57 20.32 32.27 94.83 340 5.38 3.771.61 428.00 0.04 0.21 67.75 8.93 0.07 4.79 17.51 41.62 95.58 340 10.277.19 3.08 224.34 0.04 0.21 67.05 8.95 0.07 4.87 18.06 39.79 96.25 3409.34 6.53 2.80 246.75 0.05 0.20 66.03 8.81 0.07 5.04 19.06 36.45 97.25340 8.82 6.17 2.65 261.14 0.05 0.20 64.93 8.73 0.07 5.19 20.14 32.87100.50 340 16.28 11.40 4.89 141.46 0.07 0.21 66.84 9.10 0.08 3.44 19.6634.48 101.58 340 17.09 11.97 5.13 134.76 0.06 0.22 65.59 9.03 0.08 4.5019.80 33.99 103.92 340 9.05 6.34 2.72 254.43 0.06 0.21 65.51 8.91 0.074.32 20.28 32.38 106.25 340 22.83 15.98 6.85 100.89 0.05 0.21 65.50 9.020.08 4.63 19.75 34.17

It was found that the “per pass” HFC-236ea conversion was lower thanwith nitrogen diluents. It was concluded recycled HFC-1225ye in whateverisomer blend desired could be utilised to dilute the HFC-236ea feed andproduce superior catalytic conversion of HFC-236ea to e.g. Z-HFC-1225ye.

EXAMPLE 13 Vapour Phase Isomerisation Over 6% Zn/Chromia in the Absenceof HF Including Catalyst Regeneration

A 2 g sample of amorphous 6.0% Zn/chromia catalyst was charged to a 15cm×1.25 cm Inconnel reactor tube. The catalyst was dried (250° C. for 1hour) and pre-fluorinated (N₂:HF molar ratio of 6:1 for 1 hour at 250°C., temperature ramped to 380° C., nitrogen diluent switched off andleft overnight). Following pre-fluorination the reactor was cooled. Thena mixture of 5 ml/min nitrogen and 1 ml/min of a mixture of 87.8%E-HFC-1225ye, 9.1% Z-HFC-1225ye, and the balance being a mixture ofminor amounts of HFC-227ea, HFC-236ea, HFC-236cb and hexafluoropropenewas passed over the catalyst at 130° C. at 5 ml/min whilst monitoringthe conversion of the E-isomer to the Z-isomer. After the conversionbegan to drop, the feed flow was stopped and the catalyst regeneratedusing a mixture of nitrogen (40 ml/min) and air (4 ml/min) at 380° C.for 12-16 hours. At the end of the regeneration the air feed wasswitched off and the catalyst was cooled to 130° C. When the catalysthad cooled the isomerisation cycle was repeated. The results of thisisomerisation/regeneration/isomerisation cycle are presented in Table 13below.

TABLE 13 HFC-1225ye isomeric composition % Time (mins) Z-1225ye E-1225yeCycle 1: 8 91.4 3.8 43 94.4 3.8 63 94.6 3.7 93 94.5 3.7 119 94.5 3.9 15594.6 3.9 181 92.0 3.7 213 93.1 4.0 298 89.1 9.5 335 85.7 12.6 358 79.719.2 378 76.5 22.0 Cycle 2: 10 95.0 3.7 35 94.4 3.7 70 94.6 3.8 95 94.43.8 125 94.6 3.8 150 94.7 3.9 185 94.3 4.1 215 94.0 4.7 241 91.7 7.0 27086.0 12.5 300 75.0 23.4

These experiments demonstrated, that the catalyst retained itsisomerisation activity for a significant period in the absence of HF,the isomerisation performance began to deteriorate after 4-5 hrs ofcontacting, and an air/nitrogen regeneration restored the catalyst toits original state; therefore it can be concluded the loss ofperformance was due to coking-type reactions.

EXAMPLE 14

This example demonstrates how catalyst fouling rate can vary during theconversion of HFC-236ea to HFC-1225ye as a function of pressure. 6 g(2.0-3.5 mm) of a 5.2% Zn chromia catalyst was charged to a reactor andpre-fluorination by drying it at 250° C. overnight under 80 ml/minnitrogen at 3 Barg, heating it at 300° C. and treating it with 4 ml/minHF and 80 ml/min nitrogen at 3 Barg for 16 hours, reducing the nitrogenflow to zero and maintaining it at 300° C. for a further 4 hours,increasing the temperature to 380° C. at a rate of 25° C./hour andmaintaining it at 380° C. for a further 3 hours.

At the end of the pre-fluorination, the reactor temperature was set to340° C. and the pressure set to 15 Barg. HFC-236ea feed commenced whenthe conditions had stabilised. The target feed rate was 13-14 ml/min atSTP. The reactor off-gases were routinely sampled to monitor catalystperformance. The cycle was ended, when the performance of the catalystwas approximately half of the initial performance. The catalyst wasregenerated at 380° C. with a mixture of air (4 ml/min) and nitrogen (80ml/min). Three such experimental cycles were completed at 15, 5 and 2.3Barg (3.3 Bara).

The actual mass of 236ea estimated to have been fed during each cyclewas:

236ea fed during Cycle 1 at 15 Barg=1860 g

236ea fed during Cycle 1 at 5 Barg =1637 g

236ea fed during Cycle 1 at 2.3 Barg=1540 g

Results

The results for each cycle at the different pressures are summarised inTables 14-16 and illustrated in FIGS. 6-7.

As the pressure reduced, the headline conversion increased, reflectingthe inhibiting effects of HF partial pressure on the reaction rate. Thisincreased conversion as pressure reduced was even more pronounced whenconsideration was given to the reduction in contact time that occurredas the pressure was reduced.

At 15 and 5 Barg, the rate of performance loss and therefore foulingappeared, similar. Furthermore, the rate of fouling appeared toaccelerate as the tests progressed. At the lowest pressure tested, 2.3Barg (3.3 Bara), the rate of fouling appeared. to be marginally reduced.At low pressures, conversion was higher and therefore the catalyst wasexposed to more unsaturates apparently without any detrimental effect onfouling rates.

FIG. 7 illustrates the selectivity to E and Z 1225ye during each, cycleat the 3 different operating pressures. At 15 Barg the selectivityappeared to rise, stabilise and then fall away over the cycle. At 5 Barga similar pattern of behavior was observed, although both the initialrise and final fall were less pronounced. At 2.3 Barg the selectivitywas very stable over the cycle, with no apparent fall away.

The results suggest that catalyst fouling was not strongly pressuredependent, but selectivity was maintained at low operating pressures.

TABLE 14 Conversion and selectivity data at 340° C. and 15 Barg 236eaTime Selectivity Conversion (hrs) ( %) (%) 0.4 91.9 35.6 1.1 90.1 37.92.5 87.4 39.2 3.0 86.1 39.4 3.9 88.0 38.7 22.6 89.5 28.2 27.2 89.7 38.130.3 90.1 37.9 46.7 91.8 37.0 52.7 91.3 37.3 53.5 91.5 37.5 71.8 90.545.8 72.4 91.5 37.8 73.7 91.4 37.6 76.9 92.2 36.7 93.8 93.1 34.0 94.893.1 34.9 95.3 93.0 35.4 97.3 92.8 28.8 97.7 92.9 31.6 98.3 93.0 34.199.2 92.8 35.8 100.3 92.9 35.3 101.5 93.2 34.6 103.4 93.0 34.7 104.792.8 35.2 105.3 93.0 35.5 106.4 92.9 35.2 123.3 92.6 27.9 123.8 93.032.1 124.6 93.2 33.4 125.4 92.3 36.4 126.0 93.1 33.7 127.5 93.3 33.5129.9 93.2 33.5 147.4 92.7 28.7 148.3 93.1 31.4 148.9 93.2 31.7 152.893.2 31.9 174.3 92.4 30.6 176.1 93.1 31.6 178.6 93.0 29.5 195.9 92.728.1 196.6 92.7 27.8 202.3 92.8 26.9 202.8 95.6 47.8 204.6 92.3 26.0205.6 92.3 25.9 249.0 87.2 14.4 250.5 86.3 15.9 274.5 84.9 14.5 275.587.3 14.6 277.7 91.2 20.7

TABLE 15 Conversion and selectivity data at 340° C. and 5 Barg 236eaTime Selectivity Conversion (hrs) ( %) (%) 0.7 94.2 53.6 1.4 94.7 51.82.2 94.5 51.2 18.6 95.5 47.9 20.0 95.0 52.3 20.4 95.4 48.0 22.1 95.447.8 22.9 92.9 54.8 23.8 95.5 44.4 25.0 95.4 46.3 25.9 95.3 49.9 27.795.3 49.3 28.7 95.3 51.8 29.6 95.1 49.8 31.2 95.2 50.6 47.9 95.4 50.648.6 95.4 49.9 50.0 95.5 49.4 55.3 95.4 50.1 71.9 95.6 48.6 72.8 95.547.4 73.7 95.4 49.3 75.8 95.1 51.7 96.6 95.6 49.2 97.0 95.6 48.8 97.895.6 47.3 98.4 95.6 47.1 99.7 95.5 47.8 100.9 95.6 43.0 101.8 95.7 45.7119.0 95.6 46.5 119.4 95.7 46.5 120.9 95.6 45.8 123.0 95.6 44.7 123.995.7 44.8 125.8 95.6 43.7 192.3 94.4 33.5 192.8 94.2 32.1 193.4 94.433.9 195.3 95.0 34.9 196.1 94.5 34.5 215.4 94.4 33.7 216.3 93.5 28.5217.6 92.8 25.1 219.0 93.0 26.3 219.7 93.4 27.8 220.8 93.6 28.7 222.293.5 28.2 239.0 93.3 26.4 239.8 92.6 24.7 241.3 92.3 23.5

TABLE 16 Conversion and selectivity data at 340° C. and 2.3 Barg 236eaTime Selectivity Conversion (hrs) (%) (%) 0.5 94.6 66.2 16.9 96.0 63.317.3 96.4 59.1 18.4 96.2 61.0 19.1 96.2 61.6 20.8 95.5 63.8 21.2 95.464.1 21.9 95.7 63.4 22.9 96.9 54.9 23.3 96.6 61.8 24.2 96.6 62.3 24.596.2 65.0 25.0 96.4 63.3 25.8 96.3 65.2 42.9 96.8 60.9 43.5 96.9 60.444.2 96.7 61.9 45.2 96.7 62.5 46.8 96.7 62.1 47.4 96.5 64.5 48.5 96.664.6 49.9 96.6 63.5 66.9 96.8 58.3 67.3 96.9 58.9 67.9 96.8 61.0 68.496.7 63.2 68.9 96.6 61.9 71.9 96.6 62.7 72.9 96.2 63.5 91.0 96.3 60.2114.1 96.2 64.3 116.5 96.9 59.9 121.5 96.5 59.2 139.7 95.7 63.0 140.596.4 59.7 141.7 96.2 61.9 143.0 96.1 63.6 143.5 96.3 61.9 144.2 96.163.3 144.8 96.1 62.0 145.3 96.4 61.7 146.0 96.5 59.7 146.6 96.7 58.3163.4 96.5 59.0 164.0 96.6 59.0 164.6 96.6 58.0 167.1 96.4 53.2 168.096.6 57.2 169.0 96.6 54.1 187.1 96.5 60.4 187.6 95.0 65.8 193.0 96.454.4 193.5 96.2 61.9 194.0 95.9 57.3 213.9 96.1 42.7 244.0 96.0 41.0244.6 96.0 41.1 245.7 96.1 41.6 250.7 96.3 47.3 267.2 96.3 46. 3 267.696.3 45.3 271.5 96.0 42.4 291.2 96.2 44.9 295.7 95.0 39.8 297.2 95.939.2 315.1 95.8 38.9 315.9 95.7 37.5

We claim:
 1. A process for preparing 2,3,3,3-tetrafluoropropene(CF₃CF═CH₂) comprising: (i) fluorinating 3,3,3-trifluoro-2-chloropropene(CF₃CCl═CH₂) with HF in the vapour phase in the presence of achromia-containing catalyst to produce an intermediate compositioncomprising 1,1,1,2,2-pentafluoropropane (CF₃CF₂CH₃); and (ii)dehydrofluorinating the CF₃CF₂CH₃in the intermediate composition toproduce CF₃CF═CH₂.
 2. A process according to claim 1, wherein step (ii)is carried out in the presence of a zinc/chromia catalyst.
 3. A processaccording to claim 2, wherein the zinc/chromia catalyst comprises 0.01to 25% by weight zinc.
 4. A process according to claim 3, wherein diezinc/chromia catalyst is amorphous or from 0.1 to 50% by weight of thecatalyst is in the form of one or more crystalline compounds of chromiumand/or one or more crystalline compounds of zinc.
 5. A process accordingto claim 1, wherein the intermediate composition further comprises1,1,1,2tetrafluoro-2-chloropropane (CF₃CFClCH₃).
 6. A process accordingto claim 5, wherein the process comprises fluorinating, CF₃CFClCH₃toproduce CF₃CF₂CH₃.
 7. A process according to claim 6, whereinCF₃CFClCH₃is fluorinated with HF in the presence of a chromia-containingcatalyst to produce CF₃CF₂CH₃.
 8. A process according to claim 1,wherein the ratio of HF:organics in the fluorinating step is from about5:1 to about 30:1.
 9. A process according to claim 1, wherein theprocess is carried out at a temperature of greater than 300° C.
 10. Aprocess according to claim 1, wherein the process is carried out atsuper-atmospheric pressure.
 11. A process according to claim 1, whereinthe process is carried out at a pressure in the range of 1 to 5 bara.12. A process according to claim 1, wherein the catalyst is subsequentlyregenerated.
 13. A process according to claim 12, wherein theregeneration step is oxidative regeneration.
 14. A process according toclaim 1, wherein the process is carried out with a diluent gas.
 15. Aprocess according to claim 14, wherein the diluent gas comprisesnitrogen.
 16. A process according to claim 1, whereindehydrofluorination is carried out in the presence of a feed comprisinghydrogen fluoride (HF).
 17. A process according to claim 1, wherein thedehydrofluorination is carried out in the absence of added hydrogenfluoride.